Dispensing multiple fluid components in accurate proportions has been a long standing need. Such components typically have to be kept apart until the time of dispensing to prevent premature reaction between them. Vacuum type pump dispensers and dual compartment tubes are readily available. However, differences in fluid rheology cause one fluid to flow differently than the other when such dispensers are actuated. As a result, proportions dispensed are often inaccurate. One fluid reservoir may even run out of fluid before the other.
Positive displacement pumps for simultaneous dispensing of multiple fluids in accurate proportions have become available recently. An example is the Mentadent.TM. toothpaste co-dispenser, a Trademark of Chesebrough-Pond's USA Co. of Greenwich, Conn. The Mentadent co-dispenser has an upper portion containing two cylinders, each filled with different components of a toothpaste. At the end of each cylinder is a piston frictionally engaged in its cylinder to prevent leakage of toothpaste fluid from the cylinder. The upper portion is telescopingly connected to a bottom portion having two upright posts of equal length, which are spaced apart so as to align with the cylinders of the upper portion. When a user presses downward on the upper portion, the pistons are pressed against the two fixed posts. Such pressure causes the pistons to move upward into the cylinders and to drive toothpaste fluids from each cylinder through separate discharge orifices connected to the top of the cylinders. The amount of fluid dispensed from each cylinder is determined by the distance the upper portion is pushed downward and the diameters of the two cylinders. In most cases the cylinders have a common diameter so that the same volume of fluid is dispensed from each cylinder at the same time, regardless of fluid properties. The upper and lower portions of the pump may be disengaged from one another to promote refillability, with the pistons remaining lodged in the cylinders to provide sealed product compartments.
Many commercially-available pump designs, while providing for convenient dual dispensing of two diverse products, require an interlocking geometrical relationship between the posts and piston heads to facilitate alignment during assembly. Others require such interlocking relationships to extract the piston heads from the cylinders when the halves of the pump are disengaged. In addition, the molding of precision fit parts which must engage reliably in the consumer environment is a challenging endeavor when attempting to minimize the material content of the molded parts.
Accordingly, it would be desirable to provide a dual piston, dual dispensing pump which may be readily and economically produced.
It would also be desirable to provide such a pump which provides for reliable engagement of mating parts under in-use conditions of assembly.